The synthesis of ketones by contacting carboxylic acids with various metal oxide catalysts at elevated temperatures is well-known. For example, in U.S. Pat. No. 4,754,074 Hussman describes a process for the generation of dialkyl ketones using manganese dioxide supported on alumina. The Hussman patent provides an excellent overview of the prior art up to about 1988 and provides a comparison of the various prior art catalysts useful in the generation of diethyl ketone from propionic acid. Active catalysts include oxides of lead, iron, zirconium, manganese, thorium, and neodymium, with zirconium and thorium being preferred prior to Hussman's discovery of the use of manganese on alumina catalyst.
In addition to the prior art described by Hussman, several additional prior art references describe the preparation of ketones from carboxylic acids. In German Patent 2,758,113 (1979), Froelich, et al. describe the use of thorium and/or zirconium oxides with anatase (TiO.sub.2) along with an optional additional support, such as alumina. German Patent 2,111,722 describes an improved process for the generation of ketones from carboxylic acids by the addition of steam to thorium oxide catalyzed processes. These processes and those described by Hussmann are conducted in the vapor phase. However, Japanese Patent 93/016419 (1983) departs from the normal vapor phase process and describes a liquid phase process using a zirconium oxide catalyst.
U.S. Pat. No. 5,808,148 (1998) discloses a process for the preparation of methacrylic acid by contacting formaldehyde and propionic acid in the presence of a niobium catalyst, preferably supported on silica. This process also produces very small amounts of diethyl ketone.